Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry). As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
When CMP is conducted, there is a problem of judging the planarity of wafer surface. That is, the point in time when desired surface properties or planar state are reached should be detected. With respect to the thickness of an oxide film, polishing speed etc., the polishing treatment of a test wafer has been conducted by periodically treating the wafer, and after the results are confirmed, a wafer serving as a product is subjected to polishing treatment.
In this method, however, the treatment time of a test wafer and the cost for the treatment are wasteful, and a test wafer and a product wafer not subjected to processing are different in polishing results due to a loading effect unique to CMP, and accurate prediction of processing results is difficult without actual processing of the product wafer.
Accordingly, there is need in recent years for a method capable of in situ detection of the point in time when desired surface properties and thickness are attained at the time of CMP processing, in order to solve the problem described above. While various methods are used for such detection, an optical detection method using a film thickness monitoring mechanism with a laser beam, which is incorporated in a rotary platen, is becoming the mainstream in view of measurement accuracy or spatial resolution in non-contact measurement.
The optical detection means is specifically a method of detecting the endpoint of polishing by irradiating a wafer via a polishing pad through a window (light-transmitting region) with a light beam, and monitoring an interference signal generated by reflection of the light beam.
In such method, the endpoint is determined by knowing an approximate depth of surface unevenness by monitoring a change in the thickness of a surface layer of a wafer. When such change in thickness becomes equal to the thickness of unevenness, the CMP process is finished. As a method of detecting the endpoint of polishing by such optical means and a polishing pad used in the method, various methods and polishing pads have been proposed.
A polishing pad having, as least a part thereof, a solid and uniform transparent polymer sheet passing a light of wavelengths of 190 to 3500 nm therethrough is disclosed (Patent Literature 1). Further, a polishing pad having a stepped transparent plug inserted into it is disclosed (Patent Literature 2). A polishing pad having a transparent plug on the same surface as a polishing surface is disclosed (Patent Literature 3). There is also disclosed a polishing pad having a window produced from an aliphatic polyisocyanate, a hydroxyl-containing material and a curing agent (Patent Literature 4).
Besides, a proposal is also offered for preventing a slurry from leaking out an interface (joint line) between a polishing region and a light-transmitting region (Patent Literature 5 and 6).
There is also disclosed a method for manufacturing a polishing pad, which includes placing a rod or plug of a first resin in a liquid of a second resin, curing the second resin to prepare a formed product, and slicing the formed product to form a polishing pad having a light-transmitting region and a polishing region integrated together (Patent Literature 7). However, since this manufacturing method includes inserting a transparent plug into an opaque resin remaining in a liquid state and curing the opaque resin, too high pressure or stress may be applied to the transparent plug from the opaque resin in the process of curing the opaque resin, which may cause residual stress deformation or swelling of the transparent plug. The residual stress deformation or swelling degrades the flatness of the transparent plug to make the optical detection accuracy unsatisfactory. In addition, the stress caused by the thermal contraction difference between both materials remains at the bonding interface between both materials during the forming process, so that separation may easily occur at the bonding interface, which may cause slurry leaks.
There is also disclosed an integrally-formed polishing pad having a transparent polymer material region and an opaque polymer material region placed adjacent thereto (Patent Literature 8). In the production of this polishing pad, a fluid polymer material is cured at different cure rates in the respective regions of a molding cavity so that a transparent region and an opaque region can be integrally formed. In this production method, however, the temperature control to change the cure rate is difficult so that the light transmittance of the transparent region may vary or it may be impossible to obtain satisfactory light transmittance.
Patent Literature 1: JP-A National Publication (Laid-Open) No. 11-512977
Patent Literature 2: JP-A 9-7985
Patent Literature 3: JP-A 10-83977
Patent Literature 4: JP-A 2005-175464
Patent Literature 5: JP-A 2001-291686
Patent Literature 6: JP-A National Publication (Laid-Open) No. 2003-510826
Patent Literature 7: JP-A 2005-210143
Patent Literature 8: JP-A National Publication (Laid-Open) No. 2003-507199